An optoelectronic component (e.g. an organic light emitting diode (OLED), for example a white organic light emitting diode (WOLED), a solar cell, etc.) on an organic basis is usually distinguished by its mechanical flexibility and moderate production conditions. Compared with a component composed of inorganic materials, an optoelectronic component on an organic basis can be produced potentially cost-effectively on account of the possibility of large-area production methods (e.g. roll-to-roll production methods).
A WOLED consists e.g. of an anode and a cathode with a functional layer system therebetween. The functional layer system consists of one or a plurality of emitter layer/s, in which the light is generated, one or a plurality of charge generating layer structure/s each composed of two or more charge generating layers (CGL) for generating charge, and one or a plurality of electron blocking layers, also designated as hole transport layer(s) (HTL), and one or a plurality of hole blocking layers, also designated as electron transport layer(s) (ETL), in order to direct the current flow.
In the simplest embodiment, the charge generating layer structure conventionally consists of a hole-conducting charge generating layer and a second electron-conducting charge generating layer, which are directly connected to one another, with the result that illustratively a pn junction is formed. In the pn junction, a space charge zone is formed, in which electrons of the hole-conducting charge generating layer migrate into the first and the second electron-conducting charge generating layer, wherein the second electron-conducting charge generating layer is an n-doped charge generating layer. As a result of a voltage being applied to the pn junction in the reverse direction, in the space charge zone electrons and holes are generated which migrate into the emitter layers and can generate electromagnetic radiation as a result of recombination (e.g. light).
An OLED can be produced with good efficiency and lifetime by means of conductivity doping by the use of a p-i-n (p-doped-intrinsic-n-doped) junction analogously to the conventional inorganic LED. In this case, the charge carriers from the p-doped and respectively n-doped layers are injected in a targeted manner into the intrinsic layer, in which the excitons, i.e. electron-hole pairs, are formed.
By stacking one or a plurality of intrinsic layers one above another, it is possible to obtain in the OLED, with practically the same efficiency and identical luminance, significantly longer lifetimes compared with an OLED including only one intrinsic layer. For the same current density, double to triple the luminance can thus be realized. For the stacking one above another, charge generating layers consisting of a highly doped pn junction are required.
The hole-conducting and electron-conducting charge generating layers may each consist of one or a plurality of organic and/or inorganic substance(s). In the production of the charge generating layer, the respective matrix is usually admixed with one or a plurality of organic or inorganic substances (dopants) in order to increase the conductivity of the matrix. This doping can produce electrons (n-doped; dopants e.g. metals having a low work function, e.g. Na, Ca, Cs, Li, Mg or compounds thereof e.g. Cs2CO3, Cs3PO4, or organic dopants from the company NOVALED, e.g. NDN-1, NDN-26) or holes (p-doped; dopant e.g. transition metal oxides, e.g. MoOx, WOx, VOx, organic compounds, e.g. Cu(I)pFBz, F4-TCNQ, or organic dopants from the company NOVALED, e.g. NDP-2, NDP-9) as charge carriers in the matrix.